X-over gurus: In-line BSC filter?

[johnnyrichards]

So on my project "Renu", I want to add the capability to have full BSC, or not to have full BSC. The design as is has about 2-3 db built in.

Can I safely import the combined response .frd and .zma to model the effect of an external BSC circuit on the entire network, or should I add the BSC in the woofer circuit, and have a switch between two padding resistors on the tweeter circuit?

I am hoping it is possible to just run it inline between the amp and the speaker for ease of install.

This design is my playground design. It cost me next to nothing to build so I am not afraid to tamper with it

In the future I am going to add a resistive vent, when I figure out how to do it for next-to-nothing.

[Pete Schumacher ®]

So on my project "Renu", I want to add the capability to have full BSC, or not to have full BSC. The design as is has about 2-3 db built in.

Can I safely import the combined response .frd and .zma to model the effect of an external BSC circuit on the entire network, or should I add the BSC in the woofer circuit, and have a switch between two padding resistors on the tweeter circuit?

I am hoping it is possible to just run it inline between the amp and the speaker for ease of install.

This design is my playground design. It cost me next to nothing to build so I am not afraid to tamper with it

In the future I am going to add a resistive vent, when I figure out how to do it for next-to-nothing.

You've got it right. The entire impedance and response are required if you're going to have an in-line BSC outside the system.

The best thing you could do is to first optimize the impedance by adding a network to smooth the system impedance so that it looks resistive from 200Hz on up. Otherwise, any BSC circuit you add will not have uniform effect with frequency.

A resistive vent is easy. Cheesecloth and a port.

[depthsounder]

I made a tapped inductor and use a switch to change between the different windings. I used a four pole switch so that I could simultaneously change the tweeter padding as well.

Probably the easiest thing to do would be to add an additional inductor in series with your woofer inductor, and have a switch that shorts it out when you want less BSC.

-David

[johnnyrichards]

You've got it right. The entire impedance and response are required if you're going to have an in-line BSC outside the system.

The best thing you could do is to first optimize the impedance by adding a network to smooth the system impedance so that it looks resistive from 200Hz on up. Otherwise, any BSC circuit you add will not have uniform effect with frequency.

A resistive vent is easy. Cheesecloth and a port.

Does it matter what kind of cheese? I am not too sure if I want Limburgher permeating my listening area...

Seriously though, just install a port and stuff it with cheese cloth? I am thinking it might require some experimenting to get it right..?

[johnnyrichards]

I made a tapped inductor and use a switch to change between the different windings. I used a four pole switch so that I could simultaneously change the tweeter padding as well.

Probably the easiest thing to do would be to add an additional inductor in series with your woofer inductor, and have a switch that shorts it out when you want less BSC.

-David

I might just do that, and have the same switch add a resistor to the tweeter network.

Hmmm...

[Pete Schumacher ®]

Does it matter what kind of cheese? I am not too sure if I want Limburgher permeating my listening area...

Seriously though, just install a port and stuff it with cheese cloth? I am thinking it might require some experimenting to get it right..?

A resistive vent is just that, an opening with some type of permeable membrane that will allow air to flow. Adjusting the density of the cheesecloth will allow you to basically seal off the box if you want to.

And the tapped inductor has issues all it's own. It will affect BSC, but also the crossover point. And you'll still need to equalize the impedance to a resistive load.

I'd suggest the tapped inductor in parallel with a potentiometer. That way, you can dial in where the baffle step compensation kicks in (tapped inductor) and how much BSC (potentiometer).

[PWR RYD]

Stuffing a reasonably large port with Accustuff works quite well. I did this in a car stereo sub application many years ago with great success. The transient response was fabulous.

[Dennis H]

I agree with Pete that a switchable BSC should be in front of the whole crossover, not just in front of the woofer. BSC works by cutting highs and you want it to cut the tweeter's highs as well as the woofer's highs when you flip the switch.

[Jeff B.]

You've got it right. The entire impedance and response are required if you're going to have an in-line BSC outside the system.

The best thing you could do is to first optimize the impedance by adding a network to smooth the system impedance so that it looks resistive from 200Hz on up. Otherwise, any BSC circuit you add will not have uniform effect with frequency.

A resistive vent is easy. Cheesecloth and a port.

Right. I have posted this before. The red line represents a textbook LR BSC circuit loaded with an 8 ohm resistor. The blue line is the same circuit loaded with the impedance of a small speaker - in this case I used the impedance of my Continuum. This is what this circuit would do if I simply ran it in-line with my speaker. So, if someone does not attempt to flatten the impedance of the speaker system before adding this they will not get what they are intending to get.

[johnnyrichards]

*Grumble grumble...* Guess I will do it the hard way and incorporate it into the crossover. *Grumble grumble...*

Thanks for the heads up guys!

[Pete Schumacher ®]

*Grumble grumble...* Guess I will do it the hard way and incorporate it into the crossover. *Grumble grumble...*

Thanks for the heads up guys!

You CAN do it outside the XO, IF you compensate the impedance first. Extra complexity for sure, but certainly do-able.

[johnnyrichards]

You CAN do it outside the XO, IF you compensate the impedance first. Extra complexity for sure, but certainly do-able.

I am thinking it will just be easier to build it into the crossover... It would be keen to have a switchable network but I have all of $90 in these tower speakers, any added complexity is not really worth it lol.

It is full BC all the way, baby...

[brianp]

I know some "purists" object to the idea of active EQ between the pre and power amp stages, but it offers advantages over building full BSC into a passive crossover. You don't throw away up to 6dB of sensitivity by padding the upper frequencies, but instead boost the lower range, so the amp only has to work harder in that range, rather than across the board. It simplifies the crossover design considerably. And it's more versatile -- with basic measurement capability, you can precisely tailor the amount of BSC for any speaker position in any room, and obtain a flat response at the listening position.

[johnnyrichards]

I know some "purists" object to the idea of active EQ between the pre and power amp stages, but it offers advantages over building full BSC into a passive crossover. You don't throw away up to 6dB of sensitivity by padding the upper frequencies, but instead boost the lower range, so the amp only has to work harder in that range, rather than across the board. It simplifies the crossover design considerably. And it's more versatile -- with basic measurement capability, you can precisely tailor the amount of BSC for any speaker position in any room, and obtain a flat response at the listening position.

I would love to throw a couple thousand dollars worth of electronics at these speakers, but they ain't worth it lol.

[E Biddy]

Here is a circuit that you can put between the pre-amp and the amp. It will cost about $3 to build.

http://sound.westhost.com/bafflestep.htm

[brianp]

I would love to throw a couple thousand dollars worth of electronics at these speakers, but they ain't worth it lol.

Well, more like a couple or three hundred bucks (much cheaper if second-hand) for a decent EQ that will serve you for many years, with many speakers, in many rooms. If you're mainly concerned with offsetting BSC, you can get by with a RatShack SPL meter and a disc of test tones for measurement gear.